Method for identifying tire characteristics

ABSTRACT

The present invention relates to a method of detecting growth of the dynamic tire circumference (circumferential growth or tire growth), wherein at least one reference value Ref is produced on the basis of wheel speed information, said reference value representing in particular a sidewise and/or crosswise relation of the motor vehicle wheels, and wherein the time variation of the reference value(s) is examined and, further, tire growth is detected on the basis of said variation.

TECHNICAL FIELD

The present invention relates to a method for identifying tirecharacteristics in an electronic control unit for motor vehicles.

The method of the invention allows detecting whether new tires aremounted on the vehicle.

BACKGROUND OF THE INVENTION

New tires can exhibit a constant growth of the dynamic rollingcircumference until 1.0% of the rolling circumference, in particularwhen they are operated for the first time at high driving speeds. It hasshown that the circumferential growth commences above a defined speedand lasts for a defined time. After this time the circumference does notcontinue growing, the growth of the new tire is completed. Furthergrowth will only occur upon further increase of the speed.

Especially in a per se known method of tire pressure loss detection onthe basis of wheel speed data alone (e.g. Deflation Detection System,DDS, Continental Teves AG & Co. oHG, Frankfurt, EP-A 0 983 154) it is ofgreat significance for the accuracy of the detection to precisely knoweffects that relate to the dynamic rolling circumference. Therefore, themethod of the invention is preferably implemented in a tire pressuredetection method of this type as known from the art. Initially, the DDSalgorithm collects driving data on the basis of the wheel speedinformation and calculates from this data a reference value (hereinbelowreferred to as Ref) according to the per se known principle. Clearedfrom disturbances, the time variation Ref(t) represents in aparticularly sensitive way deviations of the dynamic wheel circumferenceconditions. To begin with, the normal condition is learned after the newstart (Reset) of the algorithm. The learning phase is terminated and alearned value produced when enough rotational speed values have beenevaluated for the statistic evaluation. A comparison phase startsthereafter during which the actual detection of a pressure loss occurs.Current values of Ref are collected and averaged in the comparisonphase. When a sufficient number of appropriate values have beencollected, the averaged quantity is compared to the learned value forthe pressure loss detection. When the tires are newly inflated orexchanged in the detection phase, this fact must be reported to thesystem by hand. However, the provision of detection devices is alsopossible which signal a corresponding change in the tires (DDS-Reset).

BRIEF SUMMARY OF THE INVENTION

The method is preferably implemented as an algorithm in a vehiclecomputer to which is sent, through corresponding inputs, information ofthe ABS wheel speed sensors. In a particularly favorable manner, thealgorithm is implemented in a microprocessor-controlled brake controlunit that is already connected to the wheel speed sensors. Said controlunit is especially a control unit for conventional hydraulic brakesystems or for up-to-date ‘brake-by-wire’ brake systems such as theelectrohydraulic brake (EHB) or the electromechanical brake (EMB).

According to a preferred embodiment of the invention, learned values areproduced separately for predetermined speed ranges in the DDS algorithm.It is this way possible to detect speed-responsive effects of the tires.The speed-responsive production of learned values is preferably effectedin addition to the per se known production of learned values.

The method of the invention can be implemented in an especially simplemanner when the observed tire growth does not occur at all four wheelsat the same time. To determine the wheel at which tire growth occurs, itis preferred to evaluate several reference values that have beendetermined in different ways. Deviations will be encountered in thereference values determined e.g. sidewise, crosswise (diagonally) oraxlewise, and the joint evaluation of the deviations permits determiningthe wheel position where tire growth occurred.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an algorithm for tire pressure loss detection with adetection of new tires.

FIG. 2 shows diagrams representing the time variation of the vehiclespeed.

FIG. 3 is a detail view of an algorithm for tire pressure loss detectionwith new tire detection.

FIG. 4 is a detail view of an algorithm for the detection of tiregrowth.

FIG. 5 is a detail view of further diagrams for illustrating thedetection of tire growth.

FIG. 6 shows the schematic mode of operation of the detection of newtires.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to a first embodiment, it is first indicated to the system instep 101, FIG. 1, e.g. by way of a reset tip switch or an automaticdetection device, that pressure in the tires was changed manually (e.g.pumping up of one or more tires or mounting of tires). Now, it must bechecked whether new tires have been mounted in addition. To this end,the new tire detection function is activated in step 102 after pressingthe reset tip switch. When new tire growth is detected in step 103, thepressure loss detection algorithm is deactivated during this time instep 104. The DDS algorithm is activated again after termination of thegrowth of new tires.

FIG. 2 a) exhibits the detection by way of four tires where the new tiregrowth is already finished. Partial image b) shows the correspondingcurve variation when at least one of the tires is a new tire withcircumferential growth. The speed axis V is subdivided into speedintervals V0 to V7. Initially, the pressure loss detection methodmentioned hereinabove records in the intervals individually during alearning phase the usual running characteristics of the vehicle wheelsin different driving situations. When the learning phase is terminated,the comparison phase with the actual pressure loss detection isactivated. The reset tip switch is pushed at time t0. A new tire issuspected at t1. DDS is disabled. At t2, after a reasonable waiting timein the range of 10 to 15 minutes approximately, there is certainty thattire growth in this speed range and in the underlying speed ranges isfinished. Subsequently, DDS is reset completely so that the learningphase with the subsequent comparison phase is active again. Only with arepeated detection of a new tire (interval V6 at t3) will DDS bedisabled again, and the detection of new tires is performed as describedhereinabove.

FIG. 3 shows the mode of function of the algorithm for the new tiredetection in a DDS system in detail. The variable v_int indicates theinstantaneous speed interval. To simplify the problem, it can be assumedfor the detection that the new tire growth being detected will not occurbefore the first learned value was determined.

FIG. 4 explains the mode of function of the new tire detection indetail. The growth of the tire circumference is written downindividually for various speed intervals. The learned value for theinstantaneous speed interval is compared with the value of thepreferably averaged or filtered reference value Ref (Y-axis in partialimage a)) according to the method. The number n of the data record(samples), which has been considered in the determination of referencevalues in the respective speed interval, is plotted on the x-axis. Curve402 shows the variation of Ref during tire growth. Curve 403 shows thevariation when tire growth is lacking. For the detection of tire growthin the instantaneous V-interval, a counter Z (Y-axis in the partialimage b)) is used in each V-interval which is counted upwards when thevalue Ref is higher than the constant A. Counter Z is counted downwardswhen the value Ref is lower than a constant -A. Curve 404 indicates thecount of Z during tire growth, while curve 405 relates to the examplewithout tire growth. Number 401 designates the point of time commencingwhich the counter is counted upwards. When the counter, as illustratedin partial image b), reaches a top or bottom limit value (constant B),the flag ‘growth detected’ is set, whereby the algorithm is notified ofa detection of tire growth.

When the vehicle has been driven in a V-interval (V_(i)) for a definedtime, the algorithm assumes that the new tire growth is finished. Uponexpiry of the predefined time, the flag ‘growth finished in speedinterval V’ is set for this purpose.

Distinction Between Growth and Pressure Loss

According to the method of the invention a distinction can be madebetween a pressure loss and remaining tire growth in the followingcases:

Case 1: The effect on Ref(t) as a result of pressure loss causes a highgradient and a high absolute amount compared to the remaining tiregrowth.

Case 2: Wheel detection according to the method described hereinbelow ispossible. Case 1, for example, concerns pressure loss during vehiclestandstill after a learning operation in this speed interval or a veryquick pressure loss. It is especially preferred that the count of thecounter Z is once more counted downwards when the value of Ref reaches asecond limit value (constant C). This protects the system againstindicating growth of a new tire, although actually pressure lossprevails. The following physical relationship is assumed in case 2:Pressure losses at a wheel cause a smaller dynamic tire circumferenceand, hence, the detection of a faster rotating wheel. In contrastthereto, continuing tire growth would lead to a reduced rotational speedof the wheel. Growth in the case of detection of a fast wheel can beruled out this way. In the last-mentioned case the counter for thepressure detection ZP is counted upwards by the value 1.

Consequences of Growth Detection

When new tire growth was detected in a V-interval, the flag ‘growthdetected’ is set. In consequence of this, the counter ZP provided forpressure loss detection will not be counted further. Pressure losswarning is omitted because it is not activated until ZP has exceeded apredetermined count of the counter. When in addition growth no longertakes place in the current V-interval, the system is reset (Reset) sothat the learning phase re-commences in all V-intervals. The informationabout the termination of the growth of the new tire in the respectiveV-interval is, however, stored by means of the system.

Avoiding Faulty New Tire Detection

The function ‘recheck growth’ (301 in FIG. 3) is used as a protectionagainst a faulty new tire detection, it checks at low speeds e.g. below100 k.p.h. In these low V-intervals, tire growth can no longer occur atleast in those cases when tire growth has occurred already in a higherspeed interval.

This is based on the following findings: When in the low speed intervalthe values Ref are close to the corresponding learned values and it wassimultaneously detected that driving took place in a high speedinterval, then tire growth cannot remain from driving in the high speedinterval.

Avoiding an Incorrect Recheck

The function ‘recheck growth’ can also be incorrect when a V-intervalfor the recheck was not learned before the recheck function becameactive. A possible way out involves storing the status information aboutthe learning operation at the time when the flag ‘growth detected’ isset. The recheck function can just have been activated when the secondwarning threshold in a low V-interval was learned for which the recheckfunction is provided. It should be noted that working with the firstthreshold values can lead to errors being caused by continued learningor restarted learning in the event of incorrect learning detection.

The information about the learning status at the moment of growthdetection is stored in a variable or memory location provided for thispurpose.

Resetting (Reset) and Initialization

The system can be fully reset when a Reset was detected by the driver orby a diagnosis function. The flags for detecting the new tire growth arenot reset in the event of an internal DDS reset being possibly performedfor any other reason.

According to a second embodiment, which can be used alternatively or inconjunction with the first embodiment, the DDS pressure loss detectionmethod described hereinabove initially determines in a per se knownmanner three differently determined reference values, Ref_(diag) (FIG.6, reference numeral 6) for the relations of diagonals, Ref_(side) forthe relations of sides, and Ref_(axle) for the relations of axles. Aftertermination of a learning phase, learned values prevail for each ofthese reference values, by way of which pressure loss can be detected ina per se known manner by a comparison with currently determinedreference values. Restart of the learning phase normally starts with thedriver actuating a reset tip switch after a tire filling operation orafter replacement of the tires or wheels.

It is preferably provided in addition that after response of the methodfor new tire detection, which triggers e.g. a restart of DDS, thedetection is not activated a second time. It is thus prevented that thesystem constantly ‘learns after’ the current reference values withmultiple DDS-Resets. Pressure loss detection that is appropriatelysensitive would no longer be safeguarded in this case. Moreparticularly, a new detection is possible again only when a signal hasbeen generated for a DDS-Reset, for example after new tires have beenmounted.

The expansion effect of a new tire described hereinabove can disturb theabove pressure loss detection. Therefore, the corresponding effects of anew tire are taken into consideration in the following way.

FIG. 6 is a diagrammatic view of the mode of function of the new tiredetection. The function module ‘DDS’ (not shown) provides threedifferently determined reference values 4, 5, 6. According to themethod, the difference between an acquired learned value and a currentlydetermined (filtered) reference value is examined. When a tire grows,the corresponding wheel will rotate more slowly. This leads to a changeof the reference value for the relation of diagonals, sides and axles.The change of the three values can be distinguished from the changeduring pressure loss. In function group 1 it is found out with the aidof further differently determined reference values, which wheel exhibitsa new tire effect. This information is submitted by way of signal path 3to a probability-monitoring device 2. When the change (differencebetween the respective Ref-value and the associated learned value)exceeds a first threshold that is lower than the DDS-threshold forpressure loss detection, tire growth is suspected. The probability thattire growth exists increases by further successively determinedreference values when a current reference value likewise fulfils theabove criteria. The probability is implemented by way of a simplecounter in function module 2. When this counter exceeds a predefinedthreshold value, new tire growth is very likely to prevail. In thiscase, Reset-signals are sent to the module ‘DDS’ through lines 8, 9, 10.Line 7 temporarily disables the DDS function.

According to a preferred embodiment of the method, the reference valuefor the relation of diagonals is additionally processed by way of signalline 11. The threshold values for the evaluation of the relation ofdiagonals are set to be higher in comparison with the remainingreference values in the processing operation. It is this way possible tostill further enhance the detection reliability of the new tiredetection.

Line 12 transmits a quantity about the quality of the roadway conditionand the signal quality determined by means of the function module ‘DDS’.If the quality of the roadway or the signals is poor, the increase ofthe count of the counter is preferably suppressed when new tire growthis suspected.

Signal line 13 is provided to limit the detection of growth of a newtire to defined pre-selected kilometer readings. This function is basedon the idea that starting with a defined kilometer reading that is to befixed in an appropriate manner, new tire growth is no longer allowed tooccur. It is preferred that the kilometer reading is related to the lastDDS-Reset in order that a changing of tire will not be neglected by thesystem.

The method of the detection of growth of a new tire as describedhereinabove can also be implemented separately for individual speedintervals. When, for example, the vehicle has been driven in acorresponding speed interval for a defined time, the algorithm assumesthat the new tire growth is terminated only for this interval.Accordingly, it is also possible to learn and evaluate the referencevalues for different speed intervals independently of each other when asufficient size of memory location is available.

A distinction between tire growth and pressure loss can also favorablybe made in that a top threshold value is defined that cannot be exceededby the influence of tire growth on the change of a reference value.

Further possibilities of distinguishing between tire growth and pressureloss:

-   -   The effect on a reference value as a consequence of pressure        loss has a high gradient.    -   It is particularly preferred that the probability counter is        counted downwards when the value of Ref reaches or exceeds the        second limit value. This saves the system from indicating new        tire growth when actually pressure loss prevails.

1-18. (canceled)
 19. Method of detecting growth of the dynamic tirecircumference (circumferential growth or tire growth), wherein at leastone reference value Ref is produced on the basis of wheel speedinformation, the time variation of the reference value(s) is examined,and tire growth is detected on the basis of said variation.
 20. Methodas claimed in claim 19, wherein the reference values produced arecompared with acquired learned values, and tire growth is detected basedon the comparison.
 21. Method as claimed in claim 20, wherein learnedvalues for predetermined speed intervals are learned individually. 22.Method as claimed in claim 19, wherein the circumferential growth isindividually examined in predetermined speed ranges.
 23. Method asclaimed in claim 21, wherein it is considered in a first, low speedinterval whether circumferential growth has already occurred in a secondinterval of higher speed.
 24. Method as claimed in claim 22, wherein inthe case that the vehicle is in a predetermined speed interval forlonger than a predetermined time, it is assumed that the circumferentialgrowth in this interval is completed.
 25. Method of detecting tire airpressure loss as claimed in claim 19, wherein one or more currentreference values are compared with one or more learned values, and tirepressure loss is concluded in dependence on the deviation(s) of thereference value(s) on the learned value.
 26. Method as claimed in claim25, wherein the pressure loss detection system is deactivated whilecircumferential growth takes place or is detected.
 27. Method as claimedin claim 25, wherein the sign of the rotational speed variation of theexamined wheel is evaluated for making a distinction between pressureloss and circumferential growth.
 28. Method as claimed in claim 27,wherein the first derivative of Ref(t) and the absolute rate of thedeviation from the learned value is examined for making a distinctionbetween pressure loss and circumferential growth.
 29. Method as claimedin claim 19, wherein for determining the mounting position of the wheeldisplaying tire growth a comparison is made of the variation of or thedeviations from learned values between at least two, in particularthree, differently determined reference values, and the differentlydetermined reference values differ from each other in that theyrepresent in particular diagonal relations, side relations and axlerelations.
 30. Method as claimed in claim 29, wherein tire growth isconcluded when the at least two, in particular three, reference valuesindependently of each other allow detecting tire growth, which isespecially possible by examining and comparing the sign of the observedvariations of reference values.
 31. Method as claimed in claim 19,wherein the deviation between a reference value and a learned value forthis reference value is examined, and a probability value is raised whenthis deviation of a first threshold value DDS_FOR_GROW is exceeded. 32.Method as claimed in claim 29, wherein the probability value has aprobability threshold COUNT_GR, the exceeding of which signals that tiregrowth prevails, and the degree of probability indicated by theprobability counter depends on how frequently the threshold valueDDS_FOR_GROW was exceeded during a defined period of time.
 33. Method asclaimed in claim 31, wherein the probability value is raised only whenone or more of the additional conditions signal quality of the referencevalues, quality of the roadway condition or road section covered withina predetermined range is/are satisfied in addition.
 34. Method asclaimed in claim 19, wherein tire growth is not concluded in the casethat one or more reference values exceed a threshold value DDS_MAX_GROW.35. Method as claimed in claim 19, wherein the method of detecting newtires is reset into an initial condition when a tire change resetsignal, such as a DDS-Reset in particular, is detected.
 36. Method asclaimed in claim 35, wherein if growth of a new tire is detected, anindirect pressure loss detection system (DDS) operating on the basis ofthe wheel speeds is reset into an initial condition (DDS-Reset). 37.Method as claimed in claim 19, wherein said reference value Refrepresents a sidewise relation of the motor vehicle wheels.
 38. Methodas claimed in claim 19, wherein said reference value Ref represents acrosswise relation of the motor vehicle wheels.
 39. Method as claimed inclaim 19, wherein said reference value Ref represents an axlewiserelation of the motor vehicle wheels.